Objects in the Universe

Nebula

Nebulae are large clouds of gas and interstellar dust. They are the birthplace of stars.

Galaxy

NGC 4414 - a spiral galaxy

Galaxies are clusters of stars rotating around their centre of gravity

Main-Sequence Star

The Sun - It is ranked as G2V

Stars vary in size. Fundamentally they are dense gas clouds where the Hydogen nuclei are fused together in a nuclear fusion reaction. This creates large amounts of energy and electromagnetic radiation. They are ranked by size and brightness. Main-sequence stars are in the middle when it comes to luminosity and size.

Planet

Some planetary bodies in our solar system

Cold small body orbiting a star.

Red Giant

Red Giants are large stars that have little fusion occurring. They are very bright but do not radiate lots of heat. Less fusion occurs because large stars have exhausted their Hydrogen supply

White Dwarfs

Sirius B in comparison to the Earth

White Dwarf Stars are small dense stars where fusion doesn't occur anymore. White dwarfs are often the centre of planetary nebulas which was formed when the original star's outer layers drifted from the dwarf centre.

Binary Stars

Alpha Centauri A and B are binary stars.

Two stars that orbit around each other. Sometimes a star that is paired with a black hole. The orbits vary from a few thousand miles to several AUs.

Supernova

Crab Nebula - Remnant of supernova from 1054

A Supernova is an explosion of a star. This is when the iron core becomes so large that it's gravitational force overcomes the star and forces the protons to bond with electrons creating neutrons. The collapsing matter rebounds off the rigid core creating a huge shockwave. This in turn creates a nebula.

Black Hole

If the star is large enough it will create a black hole instead of a supernova. This is when the core is so large that its gravitational pull is so great that light can't escape its pull.

Neutron Star

A Neutron star is sometimes left behind after a supernova. They have strong magnetic fields and rotate rapidly releasing pulses of electromagnetic waves giving them their other name - pulsar

Quasar

A Quasar is a very luminous compact object. They surround a black hole at a galactic centre.

Comets

Small Ice and Rock fragments with a gas cloud (tail). Some orbit around stars normally in elliptical orbits.

Meteor and Meteorite

A Meteor is a rock fragment. When they enter the earth's orbit they heat up. They normally vaporise. Larger ones do collide with the Earth. When a meteor reaches Earth it becomes a meteorite.

Astronomical Distances

Olbers' Paradox

In the 19th century the Universe was thought to be:

Infinite

Static

Mass is uniformly distributed

Infinitely old

Olbers reasoned that if this was true then the night sky should be as bright as the day sky.

Olbers' Paradox is - The night sky should be bright because the intensity of light is inversely proportional to the radius squared and the number of galaxies is proportional to the radius squared the light reaching earth should be infinite.

He reasoned that the universe is not infinite

We now know that the universe is finite, is expanding, and the age of the universe means that the light from lots of galaxies hasn't reached us yet.

Doppler Effect - Redshift

Hubble noticed that electromagnetic waves we were receiving from galaxies followed the same spectra our sun gives off but had shifted towards the infrared section of the spectrum. Hubble determined that light waves were experiencing the doppler effect as which showed galaxies were recessing (moving away) from the Earth.

The speed of recession can be determined by the equation:

Δλ= v λ c

Δλ = change in wavelengthλ = Original wavelength of the lightv = speed of recession of the galaxyc = speed of light

Hubble created a law:

The speed of recession of galaxies from the Earth is proportional to the distance they are away from the Earth.

v = H0D

The constant in this equation is called Hubble's constant (H0)- you need to be able to change the units of Hubble's constant. They are generally found in Km per second per megaparsec. These will cancel to just per second

This helps provide evidence for the big bang as it shows the galaxies are moving from a point of origin as they are all moving away from each other and not being attracted by each others gravitational pull.

Hubble's Constant also helps prove the age of the universe

1/H0 = age of the universe

Cosmological Principle

The cosmological principle states that on a macro scale the universe is uniform and isotropic. Meaning the density is constant throughout the universe and is the same in all directions.

Background Radiation

Penzias and Wilson were recording radiowaves with a radiowave telescope from different parts of the sky. They constantly got an unwanted 'noise'.

This noise turned out to be microwaves which were constantly there at the same frequency and intensity no matter what direction the telescope was pointing.

This helped prove the Big Bang Theory - A cosmic microwave background was theorised to exist as aftermath of the big bang

Evidence For the Big Bang

Redshift - Shows all galaxies are moving apart so the universe is expanding - must come from a common originBackground radiation - Microwave remnants from the big bang - throughout universe so must have come from a big bang.

History of the Universe

Universe is infinitely dense, small and hot (Est. 13.7 billion year ago); 0s